PROJECT SUMMARY Metastatic cancers invariably relapse due to the emergence of resistant subclones that are capable of self- renewal, slow cell-cycling, tumor re-initiation and therapy resistance, termed metastasis stem cells (MetSCs). Yet the molecular mechanisms MetSCs employ for survival and regrowth are poorly understood. Preliminary data described in this proposal identify the cell-adhesion molecule cell adhesion molecule L1 (L1CAM) as a critical target for suppressing metastatic relapse. Employing novel patient-derived organoid models of therapy- resistant colorectal cancer (CRC) liver metastases, L1CAM+ cells in patient tumors are shown to selectively regenerate organoids ex vivo. L1CAM is required for the regeneration of organoids in vitro, and the mouse colon epithelium after colitis injury in vivo. Disruption of cell-cell contact in intact epithelial structures is necessary and sufficient for L1CAM induction, with expression diminishing over time as the epithelium is regenerated. We hypothesize that epithelial disintegrity induces L1CAM expression, which is required for the survival and regrowth of cancer cells during invasion, metastasis and following therapy. The mechanisms that induce L1CAM dependency during tumor progression will be defined (1) using patient-derived organoid models of metastatic CRC to define the transcriptional regulation of L1CAM downstream of epithelial junction dissociation and (2) using genetically engineered mouse models, cutting-edge organoid-derived orthotopic rectal transplantation, and orthotopic liver and lung metastatic models in vivo to determine the role of L1CAM in tumor initiation, local invasion, metastatic colonization and maintenance. The proposed investigations will delineate signaling pathways by which tumor dissemination induces phenotypic plasticity and the emergence of metastatic traits, and will pave the way for L1CAM-targeting drugs that inhibit metastasis regeneration. The applicant, Dr. Karuna Ganesh, an Instructor in the Gastrointestinal Oncology Service at Memorial Sloan Kettering Cancer Center (MSKCC), has delineated a 5-year career plan that builds upon her research background in biochemistry and clinical training in medical oncology. This project will provide the ideal training for Dr. Ganesh in using clinically representative, state-of-the-art patient-derived organoid and mouse models to dissect the transcriptional and epigenetic regulation of metastasis. Dr. Ganesh will be mentored by Dr. Joan Massagu, an internationally renowned expert in metastasis with a strong track record of training successful independent physician scientists. The candidate's career development plan includes coursework, workshops, mentoring from an interdisciplinary advisory committee comprising distinguished basic scientists and medical oncologists, and research experience in the outstanding institutional environment of MSKCC, a center of excellence in translational cancer research. Successful completion of the research project will lead to new approaches for treating patients with metastatic cancer and will provide the foundation for Dr. Ganesh to transition to a position as an independent investigator with her own laboratory and R01 funding.